In the oil and gas and some other industries there are a lot of contaminated products containing elemental sulphur and contaminants such as fine clays, sand, pebbles and gravel, and other inorganic material, as well as organic material, such as humus, wood, leaves and other vegetation. It is important to recover the elemental sulphur from its contaminants. If this is effectively done, the elemental sulphur can be recovered and the environment be improved.
The process of elemental sulphur recovery from contaminated products has been investigated for several years without full commercial and technical success. Basically, hot processes are used to melt the contaminated elemental sulphur and filter or separate by gravity to remove the contaminants from the melted elemental sulphur.
The hot remelt and filtration processes have drawbacks in treating contaminated elemental sulphur materials. Inorganic contaminants cause fouling of heat transfer surfaces in the melting process. This results in lower efficiency and high operating costs. Also, this process produces a waste product containing up to 85% elemental sulphur. In the melting process, organic contaminants adversely affect the recovery of a high elemental sulphur melt product. The most important organic contaminant is carsul which is a long chain carbon-sulphur compound formed when organic substances come into close contact with molten elemental sulphur and could result in various operating difficulties, such as fouling the process equipment and plugging the filter surfaces.
At Canterra Energy Ltd.'s Ram river gas plant a hot contaminated elemental sulphur recovery system has been studied, constructed, operated, evaluated and shut down. This system had operational problems due to fouling of the heat transfer surfaces. The maximum remelt rate achieved was 2.8 tonnes per hour over a two hour period. The filter screens required cleaning on a continual basis. The system produced an unprocessable by-product in the form of a complex sulphur agglomerate. The sulphur content of this by-product was analyzed by combustion analysis and found to contain 40-60% sulphur. The process was discontinued when operating costs could not be lowered to less than the economic threshold.
There are developments for hot processing systems which have improved waste handling methods and have increased the size of the units. However, the production of high elemental sulphur content waste products still exists.
All hot processes have the disadvantage of producing organic combinations with elemental sulphur which are objectionable and difficult to minimize or eliminate. Also, because all these processes are carried out in a hot environment, they create objectionable environmental problems.
Additionally, non-hot remelting processes have been investigated, such as:
solvent extraction in which elemental sulphur is taken into solution with a solvent;
burning the contaminated elemental sulphur to SO.sub.2 for injection to a Claus recovery plant; however, the contaminant combustion products could adversely affect the recovery plant catalyst;
use of two immiscible liquids which differentiate between elemental sulphur and its contaminants by differences in density and wettability.
The above-mentioned non-hot melting processes have not yet been developed and commercially applied in the oil and gas industry.
In this disclosure a "cold" process (as compared to melting processes) is presented for the recovery of elemental sulphur from contaminated elemental sulphur products existing in the oil and gas industry and in other industries with contaminated elemental sulphur products, which process eliminates the above-mentioned adverse factors related to hot processes and provides a higher recovery of elemental sulphur. This process, which is froth flotation, uses reagents to recover elemental sulphur as a high purity product from an aerated water and solids slurry. The solids are ground to a sufficient fineness which physically frees the elemental sulphur from the contaminants. The contaminants are primarily inorganic materials, such as fine clays, sand, pebbles, and gravel, but some organic materials are also present, such as humus, wood, leaves and other vegetation. The quantity of reagents required is very low and the reagents used are generally not objectionable from an environmental standpoint.